If the Paroches [curtain] became tamai through a sheni, you can toivel it in the Bais Hamikdash and it can be hung up even before nightfall. If it became tamai trough an av hatumah, you must take it out as with all tumah and then toivel it. You then spread it out in the chil [fenced in area] which surrounded the Bais Hamikdash.

If the Paroches was new, to show it’s beauty, it was spread out on the platform.

Shikalim 8:5

Rabban Shimon ben Gamlial said in the name of R’ Shimon ben Hasagan, the Paroches was thick as a handsbreath. It was woven with 72 threads and each thread had 24 strings. It was 40 amos by 20 amos with 820,000 threads. Two were made each year and 300 cohanim were needed to immerse it.