Filter system leaks can be a real pain for above ground pool owners. Filters are getting better over the years as are the hoses. But leaks in the filter system are still a common occurrence.
Lets start at the beginning and go through the filter system looking for leaks. Check each of these items closely for water leaks with the filter running and again with the filter turned off. Most of the time the leak will be in one of these places.
A properly installed skimmer should not leak, when they do you will see water dripping down the wall on the outside of the pool. They do not leak down the wall on the inside. You will always know if the skimmer is leaking. Most of the time a little tightening on the skimmer screws will solve the problem. If not you may need to reset or replace the gaskets. I would not try to fix the problem with silicone, although it is an option used by many people.
There is a fitting that goes into the front of the hair and lint pot. This is usually a threaded fitting. Again, you need to determine if the leak is the fitting or the hose. With all of the threaded fittings that can be installed into the filter system in anyplace I treat in this way. I first brush on some T plus 2. It is a liquid Teflon that can be purchased at Home Depot. I then wrap the fitting with Teflon tape. When prepared this way the fittings will never leak, or at least should never leak. Using a pipe wrench to get them tight is always useful.
The hair and lint pot lid is the most common cause of filter system leaks. The o-ring in the lid needs to be greased on a regular basis. If you still see air being sucked into the basket you may need to replace the lid. There are many older Hayward systems where the pot itself warps and needs to be replaced. Keep some Aqua Lube on hand and use it often in this area.
A leak in your multi port valve can usually be fixed by tightening the screws that hold it in place. The valve assembly is usually attached to the tank with ring clamp. Leaks in this area can usually be fixed by tightening the clamp. Replace the gasket or lubricate the o-ring if needed.
Inside a multi port valve is an important seal called a spider gasket. These are the most common ways to tell if it needs to be replaced. You may notice water leaking out of the back flush fitting when the system is in the filter position. You may also notice filter sand on the bottom of the pool. The valve could also become very difficult to move. These are all signs of the gasket needing changed.
Hoses and fittings coming out of the filter and back to the pool will all leak when the filter is running. If you notice leaks repair with the methods already mentioned.
The last filter system leak you may encounter will be from the drain plug in the bottom of the filter. If hand tightening the cap does not seal it try giving it a little more twist with a wrench. If it still leaks remove the cap and use Teflon tape on the threads. This usually does the trick.