After playing with different extractions, my sintered glass funnel got completely clogged with plant material (especially MHRB and harmala powder/sludge).

I tried to clean the funnel using hot water bath with soap, flushing it then with methanol with no success.

I looked around and most people use either sulfuric or nitric acid and then go to Piranha solution as the last resort. Obiously, I don't like the idea of mixing strong acid with oxidizing agent in my kitchen as it does not have a good ventilation and is overall too dangerous.

I have concentrated hydrochloric, phosphoric and acetic acids at hand as well as 30% hydrogen peroxide and strong bases (NaOH, KOH). Can any of this be used or do I really have to purchase sulfuric acid for cleaning?

I would prefer sulfuric over nitric since it has more uses (e.g. extractions) and as a dessicant.

Any other ideas on how to clean the sintered glass funnel?

I know it's not much help here (maybe something to keep in mind for the future), but in general, I believe it's best to use whatman papers when using a sintered/fritted filter. That way you don't end up clogging the filter itself, which is a real PITA to clean.

I, too, would lean towards sulfuric (I think that's what Wilmad recommends)...but perhaps a qualified chemist can chime in

Sulfuric acid + H2O2 does not form any gases of huge concern.
Generally sulfuric acid alone is "safe"(meaning if it sits in a beaker/bottle it wont do anythin wonky) because its non volatile.

Also nitric acid is best to be conserved because its so much more expensive compared to sulfuric.

You can use straight sulfuric first.
You can also try use acetic acid (>20% conc) and the hydrogen peroxide to make peroxyacetic acid but that one is real nasty and smells real bad and is also way more volatile and nasty.
But i usually go for this one if i need to rid of metal dust (Copper for example)

Hydrochlor/Phos and acetic acid wont do much on their own.

If you really dont want to buy sulfuric acid (it cheap) then you could try using KOH or NaOH but dont forget that this can damage the sintered glass by dissolving it slightly increasing pore size and more.

If you add sulfuric acid + H2O2 to a sintered glass funnel that is wet with acetone or acetic acid it will explode and send glass fragments into your body and probably kill or disfigure you. It's not 'safe' to play with.

Nevertheless, yeah filtering MHRB sludge through sintered glass is a bad idea. Its probably going to be very difficult to get it clean and working like new. The strongly oxidizing acid mixtures may be necessary. Be safe.

You cannot use KOH or NaOH to clean the frit, although they work well, they will dissolve the frit and destroy the funnel.

Using H2SO4/HNO3 would be a good idea, doesn't take much, just a few mLs. Plain concentrated sulfuric may also work just fine, just pour some into the funnel and let it soak into the frit overnight. then suck it through in the morning with water.

Before you go out and buy h2so4, try doing the same with conc HCl, see if it helps.

Thank you all.

Unfortunately the funnel has weird diameter so I could't find fitting papers and some sludge got under them anyway.

Okay I will try HCl first and then go to get concentrated sulfuric (it's cheap but hard to find a local vendor willing to sell to an individual).

What you can also do (next time!) is put a layer of white sand in the funnel before filtering sludgy biological materials, in lieu of filter paper. Obviously then you have to be a bit more careful putting the filtrand into the filter.

I meant sulfuric alone. I correct my statement to be more exact.

Also I would personally never use highly conc pirania soltions.
If you go like 50% Sulfuric and 50% 10%H2O2 you get a soltuion that will take some time to dissolve stuff but at least it wont instantly wreck everything and is thus way easier to handle/dispose.

I washed the funnel with lots of tap water, dried it and then applied small amount of Piranha solution (30 ml sulfuric acid, 10 ml H2O2, pre-made in a small beaker).

It worked perfectly and also lost most of its potency after eating through the sintered glass (tested by throwing a small piece of paper tissue in the funnel). I took lots of baking soda to neutralize, but I finally disposed it safely and left with clean sintered funnel, looks like new

Next time I will be more patient and try plain sulfuric and maybe also alcoholic KOH. I want to avoid nitric acid since I don't have any other use of it.

Dont use any caustics like NaOH or KOH with sintered glass discs.
You will dissolve the filter.
You know how lye will over time eat away at even boro beakers.
Now imagine that but with extremly high surface area.
The disc will get eaten very quickly.

I see... I watched several videos on washing glassware but unfortunately none has mentioned this. They just listed chemicals and general techniques they use in lab for washing glassware.

Unfortunately the sinter clogged again. It's a diameter I can't find proper filter discs for, but even if I use them, the plant material always finds its way into the sintered glass and nothing I have can remove it (except Piranha).

I will probably stick with Buchner funnel - the sintered glass is probably for different uses anyway...