Remember you only need to do it after every cycle unless you are real ocd or have very sludgy nutrient line that will block. If you clean a res mid cycle you will likely have to reset blumats and that's not good for the established roots nor is it any fun. I should add, if you use blumats for veg also that could be quite a long cycle depending on your flower time. Prob is with blumats you can't just turn them off as you please to clean down, not without doing damage to the exposed root mounds. You may want to look into drip clean as a preventative. Not all blumat users do this but check the details for yourself.
Warm water and a cloth, give the res a good scrub clean out over a sink or bath tub etc, the build ups are not always so visable but it's there. You may also want to invest in a black res so algae doesn't grow inside. At the very least cover that see through res with a blanket or something, so it gets no light. The blumat line once disconnected, you can hold up to the tap with your fist clenched around it to make a seal, this will force warm water down the pipe at quite a high psi and should break away any internal build ups if you hold it there for 20 seconds or so. The 3mm connector pipes/plastic fitting can be done in the same way separately. It's a pain yes but unfortunately part of keeping a clear system. If you keep your res topped up often and also use a small pond pump inside to keep the res moving this can help stop build ups on the sides of the res. The build ups normally happen when nutrients are able to dry on the side of the res or are able to settle at the bottom of the res over time prior to making their way down the line.
I don't use bleach or any such agent that is toxic during clean down but this can be your own choice.