Grindal worms are a great intermediary food between feeding BBS/Vinegar eels and feeding the much larger white worms. They can help to push your fry through from medium fry into adult size.
I use 1 litre ice cream cartons. I cut a large hole in the lid and add an equal-sized piece of sponge to it to provide aeration.
Grindal worms can live happily in green scouring pads. This is a good medium for them as it produces extremely clean worms when you harvest. A stack of 4-5 scouring pads works fine.
I feed whole porridge oats mixed with nutritional yeast. If you feed oat flour this tends to sink into the scouring pads which then means your worms migrate into the pads and become harder to harvest. As with white worms I add a small amount of tank water (~5-10mls) to moisten the oats when I feed them.
I add a piece of needlepoint plastic mesh to the culture. The worms migrate through this and can easily be scraped from the mesh to harvest.