Cars can only move at a snails pace and you will get drenched wherever you are. The roads are very dangerous. I am glad that I have experienced it but it can be a bit hairy.
The worst culprits for drenching you are the farang!

Whatever you do put money etc in a plastic bag, leave your watch, phone camera in the hotel room I would not bother with the dressing up.

I would not advise anyone to try to travel on the main day as you just don't get anywhere.

all around you will be water and people with big water cannon guns on the back of pick ups there is also the white "flour" that they throw with it.

We witnessed some Thai lad on the beach nearly drowning he was so drunk if it had not been for a number of tourist he would have.

a lot of the Thais are on holiday and they are drunk very early. There is of course the other side where whole families are out together.

worth experiencing but take precautions.

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Kiss
God laughs at people who make plans.