I’ve been steadily “improving” one of those prosumer Intex/Bestway pools the last few summers, and made quite a mess of plumbing, and my backyard in the process. 
It’s 10’ diameter, so only ~5500L, and comes with a cheap 120v impeller-driven filter/pump combo unit.
right now I’m looking for a free or cheap-as-dirt pump upgrade. either a second one of the one I have, to run them in series, or just a low-HP/flow pool/spa pump that can run on single-phase 120v, with SAE or other easily-bodged fittings I can adapt at the homey despot. if you have a line on one, please DM me here or on slack? I’m also looking for more of the OEM hoses since they’re such a hard-to-match diameter.
now on to a recap of the madness I’ve got up to so far;
When I first got the pool 2-3 years ago, I started hacking it immediately. first, I installed a skimmer I found online, it’s meant for a larger pool, but the hoses fit, so why not? it also makes a convenient attachment point for my vacuum hose, (but the suction is not so great.) The vacuum hose idea evolved, and is now a whole unit: $15 for a bag of light 1-1/4" hose, with 2 fittings, one of which threads into a PVC adapter which happens to have the same ID as the skimmer hose. the other end’s ID matches the OD of my shopvac attachments, with a friction fit.
I designed & printed a new nozzle for the pump return, it redirects the flow sideways, so that the surface debris in the pool eventually gets swirled into the skimmer.
this year, I had to put the pool on my concrete patio, so I put down several layers of carpet & underlay, both to protect the pool liner from being poked open by tiny rocks on the concrete, and to make a softer base when in the pool. I also tried to raise the steel frame with some leftover bricks to offset the drainage angle on the concrete slab, but that success was middling.
I also decided I’d finally tackle some diy solar heating. I had ~100’ of 1/2" black hose laying around from the previous homeowner’s garden sprinkler project. I also had 10x 10’ sections of 1/2" PVC laying around from when I was going to plumb in a fountain at my previous residence. Then later, as I was messing with those, I found a solar dome on craigslist for $25, and snapped it up too.
The clear plastic hoses that come with this pool, and the ports on the sides, are the first obstacle. I think they’re all metric sizes, like 31 or 33mm ID, which is incompatible with any hoses or fittings found in a hardware store aisle. I finally played around until I found that Rona stocks some drainpipe adapters in ABS that can accept the male connections, and another reducer fitting where the OD coincidentally matches the ID of the cheap plastic hoses. these and some hose clamps get me pretty far. Initially I thought that I could use the ball valve in the output as a diverter, so that closing it would increase the pressure through the solar lines, but it overloads the pump motor more than it increases the flow.
The solar dome was easier than I thought it would be, it had threaded ports, but with an unusually long unthreaded section too. I was able to slide the oem pipes over the ports, and merely seal them with hose clamps. I drive output from the main filter pump immediately into the solar dome, and then through the rest of the system.
I coiled up the black hose on a well sunlit patch of backyard, and fashioned some fittings to drive water through it from the pump circuit. i used a PVC ball valve to try and divert water into the solar loop using backpressure, but it wasn’t very successful, partly because the pump wasn’t very powerful.
meanwhile, I fashioned the PVC into a 9-leg radiator, then spraypainted it black with some leftover krylon fusion. I added a vacuum breaker on a vertical stalk too, but had to add a shutoff for that, because with the weak pump, this system currently needs the vacuum of water falling out to keep drawing in new water from the pool.
I ran the coil and the radiator in series, and then after seeing some other versions of this type of setup elsewhere, I found some old garden hose with bad ends, and used it to plumb the runs from the pool, so I wasn’t wasting the black pipe just getting to the heat. that made the coil larger too.
the return line from the solar dome hits an 1-1/2" ABS tee, the other side of which holds a diy’d one way check valve, with a 1/2" barbed fitting leading out to the 1/2" solar loop. the rest of the water goes up into 1-1/2" PVC, through the ball valve, and then back into an ABS fitting for the pool connector, and out through the 3d-printed sideways nozzle.
for water leaving through the solar check valve, the pipe goes to a manifold made from 1/2" threaded PVC fittings & ball valves where I can also input fresh water from the garden hose, and then heads uphill, into the aforementioned coil & radiator sitting above the pool in the sun. The heated water then returns via garden hose to an ABS dishwasher tee, which is also simply a manifold/adapter between the skimmer intake and an OEM Tee fitting.
And the OEM tee itself allows me to put the second intake to use with a modified nozzle, acting mainly as a safety for the skimmer, and preventing a total seal of either intake.
Here’s an album of more photos chronicling the last few years of this project, if anyone’s interested:
