In Acts 2:17,18, God pours out [ekxeo, ekxew] from [apo] his Spirit upon all people. This (alone) should be clear enough that the Holy Spirit is a thing not a person. However, let's look at all other uses of ekxeo used in the NT as listed in Young's Exhaustive Concordance.
(Mark 2:22 does not use ekxeo in the best manuscripts.)
John 2:15, "poured out [ekxeo] the coins of the money changers."
Acts 2:17, 18, God "pours out [ekxeo] from [apo] His Spirit upon all people."
Acts 2:33, "he has poured out [ekxeo] this (thing) [touto, neut.] which you see."
Acts 22:20, the blood of Stephen was poured out [ekxeo].
Ro. 3:15, Feet swift to shed ("pour out" - ekxeo) blood.
Titus 3:6, "Holy Spirit which he [God] poured out [ekxeo] upon us richly through Jesus Christ our Savior" (RSV). [This is also translated by noted trinitarian Beck as "He poured a rich MEASURE of this Spirit on us through Jesus Christ our Savior" (Beck NT)].
Rev. 16:1, 2, 3, 4, 8, 10, 12, 17, pour out [ekxeo] (the contents of) the bowls of the wrath of God. In other words "wrath" was being poured out.
Rev. 16:16, they poured out [ekxeo] the blood of saints and prophets.
Certainly in all other cases ekxeo ("poured out") refers to things. It would be unreasonable to insist that this is not the case in Acts 2 (and Titus 3:6) also. We can see that if we pour out something from something, it can mean one of two things. If we said we poured out from our bowl, for instance, we actually mean we poured from a container which contained some substance (thing). We may have poured some of it or all of it. But if we said we poured out from our wine onto your roast beef, it can only mean that we poured a portion of our wine (out of some container, of course) onto the meat. We would not say we poured from our wine if we had poured it all out.
What was it that God poured out from his Spirit? Well, what did the people receive when God poured out from his Spirit? Acts 2:4, 33 tells us they received holy spirit! If, then, God poured Holy Spirit from his Holy Spirit as described in Acts 2:17, 18, it means he poured out a portion of his Holy Spirit, as rendered in the very trinitarian translations of the New American Bible (1970 and 1991 editions ), the New English Bible, and the Revised English Bible. (It is similar to our pouring out some wine from our wine.) So God poured out some of his spirit here, some of it there, but certainly he still kept an infinite supply.
Also see Numbers 11:17, 25. The literal "from the Spirit" here in the inspired Hebrew Bible language (see the trinitarian The NIV Interlinear Hebrew-English Old Testament, Zondervan Publ.) also means "a portion" of God's Spirit was taken from one person and given to others. See these trinitarian translations of Num. 11:17, 25: RSV, NEB, GNB, AT, NAB, JB, NRSV, REB, NJB, Mo, and Byington. Spirit, then, is a thing that may be poured out in portions - you simply do not pour out persons in measured portions upon other persons!
For much more, see:
What Is THE HOLY SPIRIT? (WBTS)
Holy Spirit - Links To Information (SFBT)
Exposing the False Reasoning Behind Holy Spirit 'Proof-Texts' (SFBT)
Trinity Index (Examining the Trinity)