What’s the pit design? Does anything stop you from digging it yourself and trashing it? Alternatively dumping it into the larger reclaim tank?
Based on the price you posted you are paying for a lot of extra labor (and still overpaying a bit) or you are just way overpaying.
Depending on the volume of the wash, saturation of the vehicles and state laws much of this can change
It's a 120' long pit with a starting depth of 2' and then it slopes down to about 5' 5~" a little past the center where you get to the PVC pipes that go to the reclaim tanks (image attached of drain going off side of tunnel trench, 3 tiered reclaim tank underground). Then it slopes back up to that 2' to the end.
This is mudding country in Florida off of a beach town as well, this trench/pit fills with mud an sand within that 3 months. Enough to fill a Safety Kleen truck up every visit (3200 Gal of solids and liquids)
What stops us from doing it ourselves is that we have barely anyone to do it and nowhere to put the mud after (in bags was the worst idea lol, lots of broken bags). We actually used to shovel it out back when we didn't have such a high volume. We could just do a bit every day until it's all gone, but then the question of where to put the mud comes up. If we open the manhole and just put it in the reclaim pit, we're still going to have to pump it out anyway.