This was an accidental discovery I made tonight. I am not even entirely sure how it works but I am assuming it works like BUD switch.

When you place redstone down, the dispensers activate automatically twice. Once to dispense the lava and another time to suck it back up. This is actually quite cool cause it allows you to make obsidian faster since there's no need for you to hit the input after placing the redstone.

Now, I wouldn't be surprised if this has already been documented by someone else, I haven't seen it and I literately just accidentally made it on a SP world while trying to make one that worked with an input and a basic circuit.

Either way, for those of you that didn't know about it, enjoy a schematic to play it, for those that did, sorry to waste your time.

Additional Notes

If anyone could enlighten me on how this works or knows of any designs that are smaller/more compact, please let me know!

Also, I'm not sure if it will work if you download it, it might just be a fluke. I've since tried to replicate it and can't seem to get it to work on any new builds. So, let me know what your experience was.