We got a used pool from the mother in law and was working great. Installed it and now the valve on top of the filter is leaking out of the waste pipe. We have the Sand Dollar 150 lb. filter. I installed new sand, replaced the gasket under the valve and also the spring and still no good. It will run a little and after a few minutes start to leak out of the waste pipe intil you have a pretty good flow. What's our next step to get this going?