Frozen outflow valves (both gray and fresh water)

Hello, there has been tons written about not letting the water to freeze. But during our last winter trip, although we kept inside toasty, the outflow valves (both) froze during the ride home (long evening trip, under -5C whole time). So I got left with liquids in both tanks but unable to drain them.

Since both outflows are behind underside covers with our T6.1, it's not that easy to access them directly. The best I could think of was use of hairdryer to indirectly defrost the outflows. For the grey water, I've pointed the dryer into the hole right below the valve from the inside cupboard:



And for the fresh tank, I did the same but from the outside, pointing into those portholes in the cover:



With a huge relief, after several minutes (well, 15 in case of the grey tank), the water started to pour out.

So, the reason why I write this is twofold:
- Might come handy for somebody else in same situation
- More importantly - since I don't know much about how it looks under the covers - can somebody think of better, less tedious, way how to defrost that? Or is there something I could damage with this setup? (I've used some middle settings on the dryer, but still, I have no idea what is actually inside those areas).

Just for reference, some other threads dealing with water freezing:

Thanks, Jakub

Just an (only somewhat similar) related story..
Two years back in Schotland in January, minus 15 C. Motor wouldn't start one morning. Roadside assistance. Told us: Schotland doesn't have winter diesel (??? we also couldn't get screen wash for lower than minus 5C...), diesel filter is clogged up with coagulated parafine from the diesel (winter diesel has additives to prevent that from happening). "You just have to wait until it gets warmer", was his actual comment...
And indeed, later that morning, the parafine had dissolved again, and the motor started!

Since then, on our Schotland trips, we have a little bottle with the additive, for every time we fill her up!

Just waiting until it gets warmer would also have solved your draining problem! The 'Scottish solution'!

I don’t understand the need to thaw out the fresh water drain, as if it’s frozen it won’t get more frozen. The grey tank drain - if there’s a full tank and it must be emptied, maybe. Leave the side cover off and put the diesel heater on?

Well, only the outflows were frozen, the liquids in tanks were not at that point. So not draining will probably cost me also the water pump and maybe some plumbing as well. Might be less of a problem in case of waste tank, but the fresh has to be drained for sure.

I could leave the heater on and wait for a day when it gets above 0 (aka. Advanced Scottish Solution ), but that could last a week and it brings its own set of problems.