I don't have an issue. Two things that might help your issue:
1. Effluent tube is vertical where it drips into sump - not horizontal
2. Run my drip rate around 60 drops a minute - decent flow through. It is dialed in through the use of a ph controller - not drip rate and bubble count. Had issues in the past with clogging when I tried to control by drip count.
If it is still getting clogged at the valve, try to get one of the valves MRC uses ... I'm sure they are available from somewhere. Other valves I've used in the past had issues. MRC valve is by far the best one I've ever used ... by a wide margin.