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In an imaginary scenario, I paint with acrylics, let's say on canvas board or similar.

I don't use any fancy techniques, like impasto. Just the "normal" amount of paint and commonly used acrylic mediums.

I would like to know, whether I should be concerned about what these materials do when they get into the drain pipes (in the kitchen sink, or in the bathroom), when I wash out my brushes, and maybe some jars.

  • I know that as soon as acrylic painting materials get wet and then get a chance to dry, they end up forming a solid substance.
  • As far as I know / can imagine, drain pipes are not always soaked 100% in water, rather they have patches that get non-submerged from time to time.

Is it possible that acrylics materials could form dried-on layers within the drain pipes? That they could build up with time, decreasing the cross-section available for water flow?

Is this a valid concern? If yes, what could I do to mitigate it?

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    Whether or not it's a risk to your pipes (yes, it's likely to build up and maybe catch debris), what you pour down the drain ends up in your drinking water. Waste water treatment plants can remove solids and microorganisms, but soluable chemicals are often merely diluted. You will be among the people drinking your diluted paint. – fixer1234 Apr 13 at 3:45
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    @fixer1234 your remark does not seem to contain any mitigation suggestions. This question welcomes suggestions about mitigation techniques. Please post your ideas / suggestions in an answer; I have no doubts if your answer delivers practical / valid mitigation ideas, it will be appreciated, and will be able to help many people in the future. – Levente Apr 13 at 13:32
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In one school I went to, we had an extra part in the drain from the sink (kitchen sink style.)

From the sink the water would get into a container, the top and the bottom of the container had little walls making separate compartments and only the middle of the container had the exit to the main drainage pipes.

The heavy and very light parts of the waste 'water' would stay in the container, had to be cleaned out once in a while (I think it was once a year, but I am not sure anymore, it was quite a while ago). The light bits which would evaporate would do so and were given an escape route (likely to the outside).

This contraption was 'homemade' in the school, but we were told there were also commercial versions on the market. I would not know what to type into the search bar though, try a few if you do enough painting (and clay work) to make it needed.

This was in the early 1980s, not sure if the system would still be acceptable.

For a single person who paints some (but not a lot), I would go with the tips from the answer by Elmy, let the paint dry on a piece of paper, or use waste plastic containers to hold the rest of the paint after you are done with it. When you have used water to clean your brushes, keep the water in a pot or cup and let it evaporate naturally.

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  • That sounds very much what I am after: "simply" don't let it directly into the drain. Instead, catch it in a purposefully selected (fabricated, even) receptacle, and filter the collected liquid. In the most simplistic implementation, it doesn't even have to be a "real-time", flow-through solution. Instead, the collected liquid could be kept in a tank, and letting it into the sink through a filter could happen later, when one has time for dealing with it. That way the water could take its time getting slowly through even an incredibly fine filter. – Levente Apr 13 at 16:50
  • Of course, @Elmy's amazing advice of wiping off what one can — so that it does not even get near the sink — complements this procedure amazingly. – Levente Apr 13 at 16:51
  • The part about the evaporation could be less than universal, because in some apartments the increased humidity would be undesirable. – Levente Apr 13 at 17:01
  • Levente, if you live in such an area, you may have to make sure that the damp goes outside, either by having the evaporation done outside or under a vent. I live in an area where evaporation is slow and extra humidity is not often a problem (but we would likely use the shed if we had one for long term evaporation.) – Willeke Apr 13 at 17:04
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Yes, that concern is very valid, and it has always been a problem in any school art room I've ever been to (even though we used only water paints in school).

You should never wash big amounts of paint down the drain. The safer method is to simply let it dry and dispose of the remains in the household waste. Bigger amounts should be left to dry in a disposable container or plastic bag. Smaller amounts can be transferred to some old newspaper, paper towels, or similar disposable surface.

Brushes and mixing palettes should be wiped clean with a paper towel and then rinsed in fresh water. After you finished rinsing, continue letting the water flow for another minute to wash all the residue down your pipes. This is also useful for rinsing the pipes of old soap or fat residues (for example, after washing very oily dishes).

One solution I personally use: My mixing palette is a common glazed saucer. I let the paint that I no longer need dry on the saucer and then soak the whole saucer in water the next day. The acrylic paint won't dissolve in the water, but it will release from the glazed surface, and I can easily peel the paint remains from the saucer and dispose of them in the waste.

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  • Thank you for confirming my concern, and for the excellent and very important advice of wiping off what can be wiped off (so that the most of the stuff doesn't ever get close the drain). I wish I could mark several answers as accepted. – Levente Apr 13 at 16:55

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