They let him down by ropes. There was no water, only mud.
וַיִּקְחוּ אֶת יִרְמְיָהוּ וַיַּשְׁלִכוּ אֹתוֹ אֶל הַבּוֹר מַלְכִּיָּהוּ בֶן הַמֶּלֶךְ אֲשֶׁר בַּחֲצַר הַמַּטָּרָה וַיְשַׁלְּחוּ אֶת יִרְמְיָהוּ בַּחֲבָלִים וּבַבּוֹר אֵין מַיִם כִּי אִם טִיט וַיִּטְבַּע יִרְמְיָהוּ בַּטִּיט׃
ירמיהו לח:ו
"And they took Yirmiyahu and threw him into the pit of Malkiyahu the king's son, which was in the courtyard of the guard, and they let Yirmiyahu down with ropes. And in the pit there was no water, only mud, and Yirmiyahu sank in the mud."
Yirmiya 38:6
Rags on ropes, and a word to put them under his arms.
וַיֹּאמֶר עֶבֶד מֶלֶךְ הַכּוּשִׁי אֶל יִרְמְיָהוּ שִׂים נָא בְּלוֹאֵי הַסְּחָבוֹת וְהַמְּלָחִים תַּחַת אַצִּלוֹת יָדֶיךָ מִתַּחַת לַחֲבָלִים וַיַּעַשׂ יִרְמְיָהוּ כֵּן׃
ירמיהו לח:יב
"And Eved Melech the Kushi said to Yirmiyahu: put the worn rags and tatters under your armpits, beneath the ropes. And Yirmiyahu did so."
Yirmiya 38:12
They pulled him out.
וַיִּמְשְׁכוּ אֶת יִרְמְיָהוּ בַּחֲבָלִים וַיַּעֲלוּ אֹתוֹ מִן הַבּוֹר וַיֵּשֶׁב יִרְמְיָהוּ בַּחֲצַר הַמַּטָּרָה׃
ירמיהו לח:יג
"And they drew Yirmiyahu up with the ropes and lifted him out of the pit, and Yirmiyahu sat in the courtyard of the guard."
Yirmiya 38:13