Bert Byfield wrote:
Bert, for what purpose are you using this drywell?

Dumping gray water (kitchen sink, clothes washer). The dry well reduces
the load on the septic system. It's an old but solidly-constructed
tank, and I don't want to lose it.

Don't do it. The lint from the washer and foodstuffs from the kitchen
sink should really go to a proper septic system than can handle it by
letting it settle out in a septic tank that is pumped out at proper
intervals. A simple drywell lacks this.