Missed service because the unit was blocked by a dumpster: who pays?

You usually eat the trip fee, because the rental contract makes the site holder responsible for keeping the path to the unit clear, no matter who parked the obstruction there. The rental company's deal is with you, not your garbage hauler, so they bill you and you take it up with the hauler.

Still worth one phone call before you pay. Ask whether the driver logged a photo or a note of the blockage, whether your agreement actually spells out a missed service charge, and whether they'll waive it once if you get the next pump on the schedule quickly. I've had a fee dropped on my sites more than once just by asking politely and showing it was a one off.

There's generally no rule that they reschedule before charging. The service section of your agreement is where that lives, so read it before the call.

The real fix is placement. Ask the hauler to drop the next dumpster on the far side of the drive, and mark the truck lane with cones so nobody parks in it. The vacuum truck hose only reaches so far, so keep that lane open on service day and give the hauler a heads up the day before.

One more thing: if that unit went a full extra cycle without pumping on a busy rehab crew, ask for a service now instead of waiting for the next scheduled visit.