First off... I have a 16x32 inground vinyl pool with a 21" sand filter. One skimmer on the side, one at the pump of course, 2 inlets and no floor drain. Acouple of months ago, my 3/4 hp pump motor burned up (I knew it was coming, it was very old) so I went to my pool store to get another one. They recommended I upgrade to a 1 hp so I did. Came home, put it on, all was well and it pumped the water just a hair better than my old A.O. Smith. The next day I went to vacuum to find that I would lose my prime in about 5 minutes after I hooked the hose to the skimmer. Thought about it, decided the hose was getting old too so went and bought a new one and all new fittings. I even changed the brushes on my vac head. Hoooked it to the skimer again... it held the prime for much longer (20-30 minutes) but now I notice that it is blowing te dirt and algae back into the pool via the two inlets. Thought again. The sand hadn't bee changed in about 5 1/2 years. I figured the new pump was putting it to the test and probably time to change it again. Did that. Checked the latterals while I was in there and all looked good (I didn't take them out and inspect, just pulled it to the rim and eyebaled each one while feeling for anyting abnormal). Carefully put it all back together, hoked the vac up and...same thing. Blow back. Had a couple of beers and returned to it the next day. Started thinking that I changed the multi port about te same time I did the last sand change (5 1/2 years ago) so I opened the top of the multi port to find the spider gasket not torn or mangled but looking pretty deteriorated. So I got another one, glued in place, cleaned the handle and spring assembly and put it back together. Hooked the hose back up, same thing. I've gone over everything I can think of. There are no apparent leaks anywhere and I don't lose more than 1/4 inch of water per day (waaaay South Alabama...it's HOT!). The gasket on the auto-chlorinator looks ok but it's a little flat. I turned it to off and tried again. Same thing. I'm going to pick up another one today just in case but I'm willing to bet a case of cold ones that it's not the problem. The pump basket gasket is only a couple of months old but I cleaned and re-lubed it yesterday with no change too. I'm stumped here. Any suggestions at all would at least give me a direction now. I know I can vacuum to waste and will probably do so starting today but geesh... I don't want to continuously waste that much water, money and TIME! What am I missing?