I was reading through some old archived posts the other day (and now I can't find it) but someone mentioned they use an oil sock, someone else said they used oil eating microbes.
That being said I'm looking for recommendations too
I dump oil dry in the pit a few times, it will absorb most and sink into the sludge. If its only a small amount we use styrofoam, break into small pieces and the oil attracts to it.
There is a product on the market that looks like peatmoss. It comes in bags and specifically designed to absorb oil and hold it indefinitely. The Pennsylvania Dept of Environmental Resources told me it allows you to soak up oil then take it to a landfill and dispose of it. You can use it and put it in your dumpster. I found out after a customer drained their oil and we had him arrested for dumping the oil in our pit. I lined some old soap drums with plastic bags then scooped this oil and product up and put it in the containers and tied them shut. It supposedly will not release the oil ever. It was easier then trying to skim off the oil. You need to let it soak for several hours before scooping it out. I haven't used it in years and will try to find the old bag I had and get back on here with a product name.
I use an Oil Dri product (New Pig also has them). It's a 2x2 sheet of absorbent. It absorbs oil, not water. Just cover the top of the pit until they saturate with oil, then through them away.