[JRTJH]

No idea on how long you've had the trailer or how you're using it, but here's some suggestions:

FIRST: Post the model, year, how you're using the trailer

Without knowing the age of the trailer, I can't suggest what is a warranty item, what you need to fix and what you can just ignore because it's not worth the effort to fix it (unless you have time and extra money). That said:

As for the pressure relief valve on the water heater, when you push the lever, it's supposed to leak water. Be careful, it's going to be hot enough to burn you. If it's leaking, it's probably because you've lost the "air gap" in the water tank. When there's no air, the tank contents can't expand, so they leak out of the pressure relief valve. The owner's manual has a specific method to re-establish the air gap.

The toilet "flush ball" is not a field replaceable item. The foot pedal is, the water valve is, the ball seal is, but not the flush ball. I find it difficult to imagine how the flush ball cracked unless it was frozen or intentionally damaged from trying to hit it with something ???? Anyway, you can't/won't find a replacement flush ball because it's not intended to be replaced.

Lights in the slide? That could be anything from a blown fuse, loose connector or a bad light fixture/switch/wiring. You'll just have to do some checking/inspecting to see what you can find. If it's 120 VAC, be careful, you can get hurt.

Much of what you're reporting as problems is covered by a 2 year manufacturer's warranty (water heater and toilet). If the trailer is older than that or if it's second hand to you, did you get the owner's manuals for the items that are installed in your trailer? There are specific manuals for each piece of equipment. Almost all of them are located online at the manufacturer's site. You can google the name, model number and the owner's manual, user's manual will come up for download. That will give you a ready source of information about the items in your trailer.

Tell us about your trailer, it's foolish (and a waste of time) for us to suggest ways to fix it if it's in warranty and you've no intention of doing self repairs. Alternatively, it's a waste of time suggesting that you take it in for warranty work if it's a 10 year old trailer.... Help us help you.