I have one of the "Retro Drains" It is lying on the side of my house in a "dead pond things I've tried and didn't work" work basket.
I have a Savio Solids pump. The hose from the pump goes into a plant basket to pull the solids out. The basket sold by pond stores for underwater plants with the tiny holes is wonderful for it.
The basket sits in the back of my UBERMONGUS filtration system. It works very very well. I just thought of using the basket recently and it is so easy that I could kick myself for not figuring it out sooner. It gets all the loose stuff out. I rinse it out at the same time I rinse out the skimmer basket.
The Savio pump keeps the bottom very clean. There is no need to put a hole in the liner either but you do have a hose running through the pond.
I don't seem to lose fish in it either like I did with the bottom drain.
LBD