Hi Johncamps
First off welcome to Sunline Club. Glad to have you with us.
Now to your tank problems. It sounds like you are getting a clog into the pump from the tank. There are check valves in the pump that if they get dirt in them they will not seat and then it will keep loosing it’s prime and just sit and spin. I fought one of the Shurflo pumps once so I have worked thru the check valve dirt deal.
Before you go nuts trying to get the pump to work, then it becomes clogged up again, you have to deal with the tank. Now to the tank. What you are describing is a very big problem in my mind. Now I do work for a food company so I may be on the other end of spectrum on keeping water clean. However,
If you have green, smells bad, chucks you have a major bacteria problem. The microorganism count could be in the 10 to the 6th or 7th counts. As a fellow camper friend I would not recommend you even use that tank to wash your hands or dishes with. Water that heavily loaded can cause ill heath issues.
Now what do you do? Well it depends on how bad it is. Worst case, a new tank if cleaning cannot cure it. If you can see heavy green chucks and lots of them the normal camper sanitize may not work as the tank cannot get coated well enough all the way thru the crud. I do not know on your older model however on my 2004, T2499 the tank is held in by a metal frame and one side is bolted on. By unbolting the one side the tank will come out. If you have the tank out, then you can see all areas of it and deal with it out in the open.
You now have a 2” hole where the fill hose attaches, stand the tank up on end and try with a garden hose to blast down in there and break loose all the crud. Then turn it back over and let it run out the 2” hole. If you have a high pressure water washer, the wand may fit in that hole to help with the blasting.
Once you have tried getting it all out, then you can do a chlorine shock treatment to it. Fill the tank with about fresh water a few inches, add 1/4 cup per 15 gallons of water of unscented fresh bleach. Make sure it is unscented. If it is a 30 galls tank then you need 1/2 cup. Keep filling the tank. Let it then sit full for at least 3 to 4 hours. Then drain, flush 2 or 3 times with fresh water completely. If you can see the tank totally free of crud, then you may try to use it. It is a judgment call at this point. If there are any green or yellow curd masses left inside they will keep on growing. May have to repeat the cleaning until it is 100% crud free.
Once your past the OK I’m going to keep it and it is clean, then fill the tank with clean fresh potable water and add 1/2 cup of baking soda pre dissolved into it and let it sit for a day or 2. That will help get rid of the chlorine taste now embedded in the plastic. You can also do this step when you sanitize the entire camper.
Also before re-installing the tank check the fresh water fill hose for crud, the tank vent line and the pump suction hose. All 3 of them need the chlorine shock treatment as well.
Put your tank back on. Sunline has used food grade silicone on the large fill hose fittings. At least on mine. You can find food grade when it lists it for Aquarium use. Toxic to fish is just like toxic to humans. On the back in fine print it will state it meets a CFR number. Code of Federal Regulations. That number should takes you to the food grade regs. Do not use normal home Silicone it is not food rated. See this pic of where I bought some in Lowes/Home Depot. Sorry I can't remember which one. And only 1 carried it in our area.
Once the tank is totally clean then put it back in and redo the entire sanitize again for the camper. The tank will get a 2nd cleaning then too. Your camper is infected with the same bio load that came out of the tank. Drain and blow out the system before you sanitize the camper to get all the old water out 1st. Especially the hot water heater. If you need help on sanitizing the system, PTHutch has a good write up on it here on SOC. Have to dig a little to find it. If you can’t find it let us know, we can dig to find it too. I have to get back outside to finish up some things now or I would look too. The search featreu should trun it up. Search on "chlorine" or "bleach" should hone in on it.
Once word of caution, if you do decide to keep the tank in the camper and attempt to clean it, I would not let the crud water go thru the pump or the TT. You just put all that crud thru the pump and the check valves in the pump will not be happy. Nor you… plus you super infected the camper. Let it drain out on the ground some how.
Good luck, hope this helps and report back. We too learn from you on how you over came the problems.
John