So Many Questions...3607

It's time to explore. It's your boat, so don't be shy.
Start at your deck fittings. You'll most likely find your holding and water tanks in close relation to their pumpout/fill fittings. The fuel tanks are most likely to the outsides of your engine room if you have two or forward of your motors if one. SImply follow your fuel line from the motors.
To flush your fresh water system simply fill the tank and drain it through ALL faucets until foam disappears. It'll take several times though to clear the non-tox anti-freeze. There are also sweeteners available at your marine or RV store that will aid the taste, but bottled water is generally to order of the day for drinking.
5) Are you talking about the actual starter or the ignition switch. For the former contact an Onan dealer. For the latter there should be an ignition switch on the motor.

P.S. I'm being intentionally a little vague to encourage your exploration. This is the time to learn your boat.

P.S. "Yellowish" tanks hints at gasoline, but I'd be surprised to find them under your bunk. Most likely holding.

I have a 3607 also. Your fresh water tanks (2) are under the bed in your master stateroom, your waste holding tank is in between them. There is a plug aft and at the bottom of your fresh water tanks but flushing thru the faucets is a good method. Don't know about your Onan.

Under the bed in my 3607 is the water heater and 2 fresh water tanks.
The holding tanks are on the port side in the engine room, one aft and one foreward, both connected to a pump and thru hull for off shore emptying. This should be locked closed in fresh water.

The fuel tanks are also in the engine room, one port and one starboard.

As gto the heads, the one with the "bottle jack" is both electrical and manual and I suppose the other is just electric, but that sounds strange. Unless the previous owner never left the dock.

And yes you can get parts via Onan for you genset.

Good Luck

If your batteries are too low to flush you have bigger concerns and problems to worry about than flushing

As NYCAP suggested you have to go thru the boat from bow to stern, open evey hatch, every compartment, lift every possible floorboard and know where everything is especially bilge pumps and thru hulls, strainers and seacock

Being a gas boat, make absolutely sure you have both working CO detector in the sleeping quarters and gas fume detector in the bilge of the engine compartment. These are critical times on a gasser especially with generator

On my 3607, a 1990 model, the tanks under the master bed are 2 fresh water tanks and a waste water tank near the foot of the bed. The water heater is also under the master bed but closer to the transom. The second pump out fitting you have is for the forward head holding tank which is located under the dinette seat.

if i could suggest a couple of things just being friendly
it would be best especially for new topics to start a new post. i.e. impellers on a cruader rather than in the orignal post which is in this case rather vague anyway. epople may not want to read all of the posts and may miss new topics in the reponses

on any questions and in this case i think you will do better with more info such as what model, year, size etc of crusaders you are speaking of. try googling, there is tons of info on crusader engines an manuals to download so you will have your own reference files, pictures diagrahms etc. i would sit and google every topic you could ever think of on your boat download files and links to articles and guides and you will begin to start your own files to help yourself when needed.

impellers are going to be located on the front of the engine being driven with a vbelt and will have water inlet and outlet hose connected to them will be the first thing the inlet water from the seacock will be connected to . which impeller will be dependent on what make and model of pump is there.'

Yes if y follow the hoses from the sea cocks, you will find the strainers (water filters that you should clean by emptying the baskets) and then the raw water pump. Typically, the cover is held by 5 screws or bolts. The rubber impeller can then be pulled ideally with an impeller puller avail. From west marine although with smaller impellers you can often pry them out with two screwdrivers, be careful not to damage the housing.

On important thing that's often overlooked. When you pull an impeller make sure it s not missing chinks of rubber, if it does you have to find them. Usually thievery will be at the heat exchanged inlet just down the hose from the pump. Pull the hose and remove the debris which could be blocking the tubes.

Another thing to check is coolant level if th engines are fresh water cooled as well as for debris under the boat at the thru hull

I have had a 3607 for several years and I STRONGLY advise that, as annoying as it seems, you do exactly what others are suggesting and figure out most of the details on your own.
ie. trace the hoses from the holding tanks to verify what each tank holds. Run water and see which tank's level drops. Run the toilet and see which tank's level rises. It isn't rocket surgery.

When something goes wrong out on the water... and these are OLD boats, so something WILL go wrong... you NEED to know your boat backwards and forwards so that you can assess the situation QUICKLY and take the appropriate action to ensure everyone onboard's safety. For example, EVERY thru-hull fitting that is below the water line has a seacock valve to close the fitting. You need to know what EVERY one of them is for, where it is located, how it works,that it does work properly, and what to do if it doesn't work. Else, when something simple like an engine intake hose ruptures your boat will sink.

Much of what you are asking about will be pretty obvious when you start opening hatches and tracing wires/hoses. I remember feeling overwhelmed at first, but gradually identifying systems. Don't be afraid to use something like a paint marker to label hoses once you are SURE what they are.

If you don't have manuals, speak up. Many of us have them and can share digitally so that you aren't left guessing on things that are well documented.

Not trying to beat you up on this at all. Just acknowledging that the learning curve on the 3607 can be a bit steep, but it as absolutely necessary that you go through the process since when the boat is under your command, you are responsible for all souls onboard.

Well put, and exactly why I wrote what I did in post 2. There's no substitute for experience, and there's only one way to get that.
Many of us are afraid to open things up or take things apart, for fear of screwing it up. Better to do that at the dock on your own boat than when faced with an emergency at sea.