Wow, looks like the underside of a number of my cars over the years.
I know that grey slop - sticks to YOU like mad. At least it washes off with water.
It will last for a few days with tin cans - longer if it remains tighly clamped with no flexing and minimal vibration.
Sometimes, I have had better luck simply taking extra care to trim the tin cans, "just so" and clamping a double layer of them without that grey stuff at all. When it turns to powder and falls out, the space it occupied becomes a hole.
However, if you were happy enough with the original pipes with 25% holes, you will be please with the improvement to only 5-10% holes. Not perfect, but an improvement.
I think you need to make friends with a plumber who is good with steel pipe and fittings. For a couple of beers, you'll get it down to 98% solid, 2% holes and it will last for weeks/months/years
I know that grey slop - sticks to YOU like mad. At least it washes off with water.
It will last for a few days with tin cans - longer if it remains tighly clamped with no flexing and minimal vibration.
Sometimes, I have had better luck simply taking extra care to trim the tin cans, "just so" and clamping a double layer of them without that grey stuff at all. When it turns to powder and falls out, the space it occupied becomes a hole.
However, if you were happy enough with the original pipes with 25% holes, you will be please with the improvement to only 5-10% holes. Not perfect, but an improvement.
I think you need to make friends with a plumber who is good with steel pipe and fittings. For a couple of beers, you'll get it down to 98% solid, 2% holes and it will last for weeks/months/years