I can't fill the water tank enough before water starts nunning out the inlet

There may be a solenoid that opens like on a washing machine to divert water to the fresh water tank.

And it appears there is

https://www.google.com/search?q=jayco+34rsbs+fresh+water+inlet+manifold

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Look at where the water inlet for filling the water tank is. On tge inside of the trailer there may be a box where the pump is located.

it should have a point that looks something like a petrol cap with the word water under it

There must be a water shut off valve between the tank and the water pump. One of those hook ups will be for city water that goes direct to your tap and the other inlet is to fill the on board tank. Again check for shut off valves.

Check to see if you have a valve labeled for tank fill. It sounds like you have a single connection to use city water or fill your tank and it is in the tank fill position. The water you are seeing would be coming from the tank over flow.

What is suge? Do you mean Sewage?
Anyway, you most certainly did not hook up to the fresh water inlet properly. This will not fill any tank. Get your manual out and read it.
Contact your local service center directly or online here:

Yes. Open the outside panel, usually located close to or beside the city water inlet. Should be a diagram showing "normal", "tank fill" and "winterize." Use "fill" to fill the tank. Water will run out the underneath drain when full. I recommend a water pressure limiter just in case the city water pressure is excessive. You can rupture a line or the tank if too high. Rare, but it does happen.

Flip the valves to "normal" to use the city water. If boondocking, the pump will pull from the fresh water tank directly. No need ot change anything.

there is probably a stoppage in the relief opening. should be next to the potable water fill. are you trying to fill from the pressure inlet or potable fill inlet? if from the pressure inlet, there is a bypass valve by the fresh water tank to divert watr into it.

There should be a fresh water fill on the outside of the coach. If not then there is a valve that would need to be turned that will allow water to be put into the fresh water tank. If that is the case then it will be a bit more difficult to put bleach into the fresh water tank but not impossible. There will be a pump that draws fresh water out of the tank. You can disconnect the input and output lines. Connect the input line which comes from the fresh water tank to the output side of the pump. Then using a flexible line with a 1/2" pipe thread fitting, connect that to the input side of the pump. Put the loose end of the flexible line into a gallon of bleach and turn the pump on. It will draw the bleach out of the container and pump it into the fresh water holding tank. Now return the plumbing of the pump back to the original configuration. Using the valve system complete filling the fresh water tank with fresh water and allow to sit for a couple of days. Then open the low point drain on the fresh water tank and completely drain. When the coach is not in use make sure the tank is completely drained. There is also a fresh water treatment that you can purchase at your local rv parts department.