1st post from a long time lurker, the tip helps keep the crud out of bikes with rear facing seatclamps but only really works on those using an allen bolt and not a QR.
1. Take seatclamp off frame.
2. Stretch 10cm (ish) of roadie innertube (snugger fit than 2.5' mtb innertube!) onto seat tube and roll down.
3. Tightly ziptie bottom of innertube at seattube/ toptube join.
4. Replace seatclamp and put seatpost in frame, adjust and tighten.
5. Stretch innertube over seatclamp and up seatpost.
6. Ziptie top of innertube(if required - depends on tightness of innertube).
7. If you want to raise and lower the seat its better to use a wider innertube and rely on the zipties (reusable) to make the seal.
A handy winter tip I reckon