OK, I think I got it. A cart has two openings, in and out. A sand filter has three, and they all go through the 6-way valve that's part of it: In, Out, and Waste.

The skimmers and drain flow to the pump, through the pump's basket, then out the pump into the filter's intake. The filter's output goes to the pool's return. The waste can either have a hose that gets rolled up, or can be permanently hooked to a drain. That's really all there is.

For every person who likes Bacquacil you'll find 10 to 20 who hate it. It's a large reason for your problems. Backwashing sand is a snap, especially if you have it plumbed into a drain. But switching to chlorine will save you a ton of money and be less work. Very few people are actually bothered by chlorine--that's a fairy tale. What bothers them is a poorly maintained chlorine pool--and if you follow the rules here you'll never have that problem. Nobody is EVERY irritated in my pool--because I follow the simple rules. The bac will goop up your sand filter too, and you'll have to replace the sand. I'd convert to chlorine, complete the conversion, then put in the sand filter.

We have been adding DE to our sand filters, a number of us, with EXCELLENT results. You add 1/3 to 1 cup every time you backwash. I started over a year ago, and am still using the first 5 pound bag in the 10 pound box--which cost me all of 8 bucks. Another 5 bucks spent on a set of Skimmer sock clones and my filtering gets even better faster.

DE IS better at filtering than sand, it IS slightly more work, but with DE in the sand and the skimmer socks, I have NO complaints.

If you are Handy Andy, putting in the sand filter should be easy. If you are all thumbs and the only nail you can hit is the one on your thumb, then you'd better get help. It's easier if you use TigerFlex flexible PVC than the hard stuff, but the hard PVC is pretty easy to work with too. With TigerFlex, you use glue-on fittings just like the hard PVC...don't be conned into using internal fittings and hose clamps--TigerFlex isn't made for them and always leaks. Use ONLY fittings rated for Schedule 40 or higher (Schedule 80 is OK but expensive). Spring for LOTS of quick releases--they make life SO much easier.