A trip to the hardware store could get you a short length of 1/4" copper tubing, a compression to pipe thread fitting, and a pipe thread to hose thread adapter. Add a hose shut off valve and you will have it. The copper tubing can be bent to the shape you need to get around inside the tank.
And, at the price of copper now, you could have your own DIY tank cleaner for no more than maybe 5 times the cost of the one from Camping World! (That's MY kind of project!)
- Jack