Here is a comparison of the pointed and unpointed text of 1 Kings:
וְעָבְיֹו טֶפַח וּשְׂפָתֹו כְּמַעֲשֵׂה שְׂפַת־כֹּוס פֶּרַח שֹׁושָׁן אַלְפַּיִם בַּת יָכִֽיל
ועביו טפח ושפתו כמעשה שפת-כוס פרח שושן אלפים בת יכיל
The word in bold, אלפים, means simply "thousand." Thousand or two thousand is determined by how the word is pronounced:
Two thousand: אַלְפַּיִם
The original text, without vowels means thousand or two thousand. The pointed text reflects the oral tradition to pronounce the word as two thousand; this is supported by some LXX manuscripts:
καὶ πάντων τα οπίσθια εις το ένδον και το πάχος αυτής παλαιστής και το χείλος αυτής ωσεί έργον χείλους ποτηρίου βλαστόν κρίνον δύο χιλιάδας χόεις εχώρει
δύο χιλιάδας is specifically two thousand. Unlike the Hebrew אלפים which could correctly pronounced either as thousand or two thousand.
This is not true of the passage in Chronicles:
עָבְיֹו טֶפַח וּשְׂפָתֹו כְּמַעֲשֵׂה שְׂפַת־כֹּוס פֶּרַח שֹֽׁושַׁנָּה מַחֲזִיק בַּתִּים שְׁלֹשֶׁת אֲלָפִים יָכִֽיל
ועביו טפח ושפתו כמעשה שפת-כוס פרח שושנה מחזיק בתים שלשת אלפים יכיל
Here שלשת which means three is added to אלפים and the text in Chronicles is specific: 3,000.
Chronicles also includes the word מַחֲזִ֣יק. It means to be strong, to make strong, or to hold strongly. One could see the intent is to describe the overall capacity (i.e. "hold strongly" = "filled to capacity") and 3,000 baths was the total capacity. Then the difference in Kings could be functional. The sea had the capacity to hold 3,000 but was only filled to "thousand" (either 1,000 or 2,000). Chronicles (4:6) also states the priests washed in the sea. In that case the water level would intentionally be left below capacity allowing for the natural rise when a person entered. Also, the daily level might need to vary because of the height of the priests scheduled that day. 1
Another possibility is given in the Jamieson-Fausset-Brown Bible Commentary:
It has been suggested that there is here a statement not merely of the quantity of water which the basin held, but that also which was necessary to work it, to keep it flowing as a fountain; that which was required to fill both it and its accompaniments. In support of this view, it may be remarked that different words are employed: the one in 1Ki 7:26 rendered contained; the two here rendered, received and held. There was a difference between receiving and holding. When the basin played as a fountain, and all its parts were filled for that purpose, the latter, together with the sea itself, received three thousand baths; but the sea exclusively held only two thousand baths, when its contents were restricted to those of the circular basin. It received and held three thousand baths [Calmet, Fragments].
The passage in Chronicles is more specific on three points:
- Three thousand, not thousand possibly meaning two thousand
- The additional term מַחֲזִ֣יק
- The information about the priests washing (4:6)
Given the potential ambiguity of the word used in Kings, and the Chronicler's decision to include additional information consistent with a larger number, I conclude the sea could hold as much as 3,000 baths and was filled to different capacities (1,000-2,000) when used.
1. A description of the functional water level would need to vary as a single level might not work for all priests: the actual amount of water used would depend on which priests were scheduled to work. A word which could mean either 1,000 or 2,000 would reflect this.