Supplement to my last post:

I checked The Espresso Shop U.K. website and they list the "border" diameter of the 14g-16g and 9g IMS competition baskets for the La Pavoni Millennium group. Both are 60mm. That's exactly what I measured with the LP single group I got. The Picopresso stock basket border is about 58.5 mm.

Thanks for your detailed comments Peppersass, that's really helpful. I currently have no way to do exact measurements.

An update, just this morning I had my first non-leaking espresso with the Picopresso plus IMS competition La Pavoni post millennium 14-16g basket.
I used 17g coffee and a puck screen, just as I've done previously with the stock basket. Even though the IMS basket is a bit shallower, it is wider at the bottom, so should hold pretty much the same amount.

The only difference this time was that I tried to screw the bottom portafilter part very very tight, much more than I would with the stock basket. No leakage, and now I get some crema (I don't expect a lot from my current beans) and the taste was also very noticeably improved. I look forward to testing it again with one of my usual espresso blends, but that's still a bit too soon after roasting.

Tightening it that much isn't ideal, it makes it quite hard to open it up again compared to the stock basket which doesn't need an extremely tight fit. But on the plus side, because no hot water leaks out, at least I could unscrew the bottom without burning my hands.

A simple yet less than ideal solution. I tried tightening it before but not nearly as much. I'll see if I can get repeatable leak-free results with this.

I couldn't find any other 51mm basket that is supposed to fit, so I'm not sure if there are other ones that may be more compatible. In an ideal world Wacaco would offer custom made IMS level quality baskets, even if sold separately or as a more expensive choice on checkout.

Re the stock funnel, it doesn't fit as well to the Pavoni basket, but for me it's still good enough. I want to keep the portable form factor (I'm using the Picopresso at work, at home I have my Cafelat Robot), so the stock funnel doesn't bother me enough to justify a replacement.

And another update to the Picopresso with IMS competition La Pavoni post millennium 14-16g basket. I'm back to my usual espresso blend, and even though I screw the basket in really tightly, in probably 4 out of 5 attempts I get clear water leaking out the sides which results in a watery, underextracted shot with minimal crema. With the previous coffee blend this didn't happen as often, but I guess because this current blend requires a finer grind, the puck created higher resistance and so the water can still find a way out the sides.

I'm starting to think that it just doesn't work for me. With other blends this may be less of a problem. I'll keep trying a bit longer, but if I keep getting 80% unsatisfying shots due to the third party basket (even though when it does work the result is really nice) then I may go back to the stock basket.

One last attempt could be to try to lift the IMS basket up a bit, for example with a silicone seal ring between basket and the screw bottom portafilter, so that the actual seal on top of the basket will fit tighter. I'll see if I find something that fits.

With the Pavoni basket that I used on my Picopresso the problem is that it is a bit wider than the stock basket and can get a little stuck on the side. But I never had problems with it not sealing. Can you easily move the basket into the Picopresso? It could be that it does not get pushed evenly against the gasket.

Hi Marmot, yes, I can easily move the basket into the Picopresso, it doesn't seem to get stuck. When the basket is in the screw bottom part (not screwed in) it can wiggle very very slightly compared to the stock basket. I would assume that with the pressure of screwing it in that shouldn't matter, but I can't tell if it doesn't lock in on a slight angle which could explain the leakage.

I tried to put some rubber rings under the edge of the pavoni basket, to lift it up by a millimeter or so, and that improved (but not 100% solved) things, i.e. it's leaking less, but there's still some clear water coming out. It already tastes better and has better crema though.

I'll try again tomorrow with a 52mm seal ring under the edge. I can't think of any other way to fix the problem than lifting the basket up a bit to get a tighter seal. I'll post an update when I tried that.

Have you checked whether the top surface of the basket is even? The gasket of the Picopresso should make an even better seal than the one on the Pavoni since it is softer.

Yes, the top surface of the IMS basket is even.

In the meanwhile I got some 52mm inner diameter seal rings and that seems to fix my issue. Each ring is just 1.8mm thick, so I added 2 just to be sure, but apparently it pushed the basket up just enough to seal properly.

These rings are just 1.8mm thick, so I added 2. I think one ring of 3 or 4mm thickness would be better. Or a metal ring or wire perhaps, there's no real need that whatever pushes the basket up needs to be flexible material. These rings are made of nitrile rubber, at least they stay in place.

I've seen online that some Picopressos (Picopressi?) can develop a leaking issue around the pump, but fortunately that doesn't seem to be the case here.

Has anyone tried the single basket that Wacaco sells? Is it comparable in quality and usability (e.g. funnel compatibility) with the regular basket that comes with the Picopresso?

I have a IMS basket too and I filed down the diameter manually. I understand that the additional seal is a solution too.
Anyway, if someone wants to decrease the diameter someone used a belt sander and I would guess that a lathe would be a good tool.

Hello, after my picopresso portafilter stuck the solution i found was to put a tiny needle into all the holes. What happened is that the holes were completely clogged and eith the needle they went free.
Beware of your eyes because a little ammount of coffee will come out of the free holes and it really hurts.