I think they come from the sewer.

Any good tips? There is like 50 of them every day

They're called Moth Files or Drain Flies - hint in the 2nd name where they come from.

If you google bathroom flies or the above you'll find a lot of info on eliminating them. Examples -

http://lifehacker.com/5826486/how-to-get-rid-of-drain-flies

http://www.orkin.com/flies/drain-fly/

I have the same problem. They seem to come at a certain time of the year for a few months, and then gone until next season.

Same problem here....flatten them.....

That fix the problem for 1 hour

Find dead body.. remove.

totster

Cross your legs.....

Encourage your Mrs to stop wearing knickers.

It'll not get rid of the flies but at least they'll be gathered in one place.

Try a drain cover that has a small water barrier.

I don't know the English name but here's a picture :

I know they are available here in Thailand.

Yermanee

Try a drain cover that has a small water barrier.

I don't know the English name but here's a picture :

I know they are available here in Thailand.

Yermanee

Found the name : its a Bell Trap Drain

As said readily available.

Yermanee

Normally live in drains - so make sure your water traps have not dried out by tipping water in the bathroom floor drains. Clean out all drains with bleach or hot soapy water. But they can also be breeding in plant pots or other damp areas. Panels around a bath should be removed to see if there's any wet areas or leaks.

Familyonthemove, on 12 Mar 2013 - 21:18, said:

Normally live in drains - so make sure your water traps have not dried out by tipping water in the bathroom floor drains. Clean out all drains with bleach or hot soapy water. But they can also be breeding in plant pots or other damp areas. Panels around a bath should be removed to see if there's any wet areas or leaks.

yes I think they don't like it dry if it get total dry they may die.

maybe a liter or two of boiling water down the drains every day, for a week, will solve the problem? Just an idea . . . .